In recent years, in power converters used for high-voltage use, for example, a power system, multilevel converters each including a plurality of converter cells, which are connected in multiple series, have been put to practical use. Those converters are called a modular multilevel converter (MMC) system, a cascaded multilevel converter (CMC) system, or the like. In the related art, there is known, for example, a system in which a converter cell is formed of a semiconductor switching element, for example, an IGBT (see Non Patent Literature 1, for example).